1Department of Land Resource Science University of Guelph, Guelph, Ontario N1G 2W1
²Aquatic Ecology Division National Water Research Institute Burlington, Ontario L7R 4A6

North Point is a 2-3 km wide promontory underlain by crystalline Paleozoic carbonates and locally, in swales, by gray silty shales of the early post-glacial Tyrrell Sea. Several environments have developed around the promontory ranging from intensely ice-gouged rocky intertidal areas on the crest, to wide tidal flats and marshes in protected areas to the north, and wide sandy flats locally separated from the marshes by longitudinal beach ridges to the south. Much of the southern tidal flats are protected from intense storms by an intertidal shoal (outer ridge) located approximately 2 km offshore and running at a high angle from the mainland. In its landward flank, the outer ridge encloses a 500 m wide elongated shallow subtidal Zostera marina zone that is followed by the maximum extension of the southern tidal flats and the salt marsh.
    The physico-chemical properties of the intertidal and salt marsh sediments biological processes are strongly influenced by tides, and many exhibit lateral gradients associated with the frequency and duration of tidal inundation. Negative correlations between sand systems and silt content (r = -0.846, p < 0.001), and positive correlations between clay content and elevation (r = 0.7097, p < 0.01) reflect the well developed sequence of landward fining in grain size which is directly related to tidal deposition. In the salt marsh the sediments are also affected by vegetation, topography and drainage pattern. Strong seasonal changes occur in chemical properties of the sediments, but there are nonetheless well-defined trends. Elevation of the marsh is positively correlated with organic carbon content (r = 0.613, p < 0.01), and negatively correlated with pH (r = -0.780, p < 0.001) and electrical conductivity, although this last variable varies greatly depending on tidal inundation, precipitation and evaporation. There exist strong lateral differences in average Eh, which are associated with various drainage patterns. Reducing conditions are consistently recorded in marsh zones which retain standing water, have high electrical conductivities and are subject to frequent tidal inundation.